EP1042845B1 - Antenna - Google Patents

Abstract

An antenna of the type comprising a first electrically conductive surface (12), a second electrically conductive surface (14) forming a ground plane parallel to the first electrically conductive surface, and a first electrically conductive feed wire or strip (16) is provided. The first electrically conductive feed wire or strip (16) links a first terminal of a generator/receiver (20) to the first electrically conductive surface (12). A second electrically conductive feed wire or strip (17) links a second terminal of a generator/receiver (20) to the second electrically conductive surface (14). At least one electrically conductive wire or strip (18, 19) links the first electrically conductive surface (12) and the second electrically conductive surface (14). The first electrically conductive surface, the second electrically conductive surface, and the at least one electrically conductive wire or strip (18, 19) linking the first and second electrically conductive surfaces (12, 14) are all coplanar.

Description

The present invention relates to the field of antennas.

• une première surface électriquement conductrice, généralement dénommée « toit capacitif »
• une deuxième surface électriquement conductrice formant plan de masse, parallèle à la première,
• un premier fil ou ruban d'alimentation électriquement conducteur qui relie une première borne d'un générateur/récepteur à la première surface et un deuxième fil ou ruban d'alimentation qui relie une seconde borne du générateur/récepteur à la seconde surface, et
• au moins un fil ou ruban électriquement conducteur qui relie les deux surfaces précitées.

More specifically, the present invention relates to the field of antennas operating in a particular mode comprising:

• a first electrically conductive surface, generally referred to as a "capacitive roof"
• a second electrically conductive surface forming a ground plane, parallel to the first,
• a first electrically conductive wire or ribbon connecting a first terminal of a generator / receiver to the first surface and a second wire or ribbon supply that connects a second terminal of the generator / receiver to the second surface, and
• at least one electrically conductive wire or tape that connects the two aforementioned surfaces.

Examples of such antennas are described for example in documents FR-A-2 668 859 and EP-A-667 984.

In document FR-A-2 668 859, an antenna of the aforementioned type comprising a single wire or ribbon connecting the two surfaces, which wire or ribbon is arranged to be traversed by a current at the frequency of work and to be coupled by inductive coupling to the wire or ribbon power supply connecting the generator to the first surface. It has been shown that this antenna generates, under certain conditions of arrangement of elements, a monopoly type of radiation, that is to say comprising a symmetrical lobe of revolution, with maximum radiation parallel to ground plane and zero radiation perpendicular to the antenna, linear polarization with electric field in a plane perpendicular to the antenna and cover almost hemispherical except in the axis.

EP-A-667 984 describes a variant of this antenna comprising several parallel wires or ribbons connecting the two surfaces. This provision makes it possible, in particular, to facilitate the adaptation of the antenna to the generator.

Antennas of the aforementioned type have already rendered great services.

The object of the present invention, however, is to propose a new antenna that can take smaller dimensions compared to the working wavelength not only in the horizontal plane as the antennas described in documents FR-A-2 668 859 and EP-A-667 984, but also in the vertical direction where the height is very low of the order of λ / 200.

This object is achieved in the context of the present invention by means of a antenna of the aforementioned type, characterized in that both surfaces and the or the wire (s) or bonding tape (s) therebetween are all coplanar.

If necessary, at least the wire or ribbon connecting the generator / receiver and the first surface is also coplanar with aforementioned elements.

• la figure 1 représente schématiquement la structure générale d'une antenne conforme à la présente invention,
• la figure 2 représente le schéma équivalent de cette antenne,
• la figure 3 représente la réponse de cette antenne en fonction de la fréquence et situe le point de fonctionnement,
• la figure 4 représente un mode de réalisation particulier de la présente invention,
• la figure 5 représente l'évolution de la partie réelle de l'impédance d'entrée, en fonction de la fréquence, relevée sur une antenne conforme au mode de réalisation illustré sur la figure 4,
• la figure 6 représente l'évolution de la partie imaginaire de l'impédance d'entrée, en fonction de la fréquence, relevée sur une antenne conforme au mode de réalisation illustré sur la figure 4,
• la figure 7 représente l'évolution du coefficient de réflexion qui en résulte, en fonction de la fréquence, pour une antenne conforme au mode de réalisation illustré sur la figure 4, (on notera que sur les figures 5, 6 et 7, les valeurs théoriques sont illustrées en traits pleins, tandis que les valeurs mesurées sont illustrées en traits interrompus), et
• les figures 8, 9 et 10 représentent le gain intrinsèque de l'antenne en dB selon différents plans.

Other features, objects and advantages of the present invention will become apparent on reading the detailed description which follows and with reference to the appended drawings, given by way of non-limiting example, and on which

• FIG. 1 schematically represents the general structure of an antenna according to the present invention,
• FIG. 2 represents the equivalent diagram of this antenna,
• FIG. 3 represents the response of this antenna as a function of frequency and locates the operating point,
• FIG. 4 represents a particular embodiment of the present invention,
• FIG. 5 represents the evolution of the real part of the input impedance, as a function of frequency, taken on an antenna according to the embodiment illustrated in FIG. 4,
• FIG. 6 represents the evolution of the imaginary part of the input impedance, as a function of frequency, taken on an antenna according to the embodiment illustrated in FIG. 4,
• FIG. 7 represents the evolution of the reflection coefficient which results, as a function of frequency, for an antenna according to the embodiment illustrated in FIG. 4 (it will be noted that in FIGS. 5, 6 and 7, the values theoretical values are shown in solid lines, while the measured values are shown in broken lines), and
• Figures 8, 9 and 10 show the intrinsic gain of the antenna in dB in different planes.

• une première surface 12 électriquement conductrice, généralement dénommée « toit capacitif »
• une deuxième surface 14 électriquement conductrice formant plan de masse, parallèle à la première,
• un premier fil ou ruban d'alimentation 16 électriquement conducteur qui relie une première borne d'un générateur/récepteur 20 à la première surface 12 et un deuxième fil ou ruban d'alimentation 17 qui relie une seconde borne du générateur/récepteur 20 à la seconde surface 14, et
• au moins deux fils ou rubans électriquement conducteurs 18, 19 qui relient les deux surfaces précitées 12 et 14,

les deux surfaces 12, 14 et les fils ou rubans de liaison 16, 17, 18 et 19 assurant la liaison entre ces surfaces 12, 14 et le générateur/récepteur 20 d'une part et entre ces surfaces 12, 14 d'autre part, étant tous coplanaires selon la caractéristique essentielle de la présente invention.FIG. 1 shows the general architecture of an antenna 10 according to the present invention, comprising:

• a first electrically conductive surface 12, generally called "capacitive roof"
• a second electrically conductive surface 14 forming a ground plane, parallel to the first,
• a first electrically conductive wire or strip 16 which connects a first terminal of a generator / receiver 20 to the first surface 12 and a second wire or power strip 17 which connects a second terminal of the generator / receiver 20 to the second surface 14, and
• at least two electrically conductive wires or tapes 18, 19 which connect the two aforementioned surfaces 12 and 14,

the two surfaces 12, 14 and the connecting wires or strips 16, 17, 18 and 19 providing the connection between these surfaces 12, 14 and the generator / receiver 20 on the one hand and between these surfaces 12, 14 on the other hand , all being coplanar according to the essential feature of the present invention.

The first surface 12 can take any geometry. This geometry and the size of this surface 12 are however characteristic of the operation of the antenna.

The second surface 14 forming a ground plane surrounds partially or completely the first surface 12. According to the schematic representation given in Figure 1, the ground plane 14 has the form of an open ring which almost completely surrounds the surface 12. The opening 15 formed in the ground plane 14 serves as a passage for ribbon 16.

According to the representation given in the appended FIG. 1, provision is made two ribbons 18 and 19 connecting the surfaces 12 and 14 together. indicated in the document EP-A-667 984 in this case the ribbons 18 and 19 are preferably symmetrical with respect to the feeding tape 16, and for example parallel to this one.

Alternatively, however, one can provide a single ribbon to ensure the connection between the surfaces 12 and 14. An embodiment will be described thus comprising a single supply ribbon for interconnecting the surfaces 12 and 14, with reference to FIG.

According to still other variants, the antenna according to the invention can include more than two ribbons 18, 19 to ensure the connection between surfaces 12 and 14.

Such an antenna can be obtained by different processes of manufacturing.

By way of nonlimiting examples, this antenna 10 can be cut in a conductive plane, preferably a metal plate, for example by etching the metallization of a single-sided printed circuit, or still by serigraphy on an electrically insulating support, deposit on a such an electrically insulating support, or production from a foil metallic geometry adapted.

Antennas according to the present invention can operate at all frequencies.

The dimensions of the antenna in the metal plane are of the order from λ / 6 to λ / 5 where λ represents the working wavelength.

Those skilled in the art will understand that the thickness of the antenna is to her, extremely small. This thickness corresponds to the thickness of elements 12 to 19 and the support thereof.

The antenna is adapted to the impedance of the generator 20 (in general 50 Ω) on the working frequency band to obtain a T.O.S. acceptable, preferably between 1.5 and 2.

FIG. 2 shows the equivalent diagram of this antenna.

This equivalent diagram comprises a cell comprising a capacitance Cfond, a Lfond self and a Resistance Rfond, connected between they in parallel and corresponding to the fundamental mode, another cell having a capacity Ctoit and a self Lmasse connected together in parallel and Lalim linkage inducing a serial link between two aforementioned cells, the self Lalim being coupled with the Limasse self by a mutual inductance M.

This is the capacity between the two surfaces 12 and 14 measurable in static mode.

Lmasse represents the inductance related to the (x) ribbon (s) 18, 19.

Lalim represents the inductance related to the supply ribbon 16.

Mutual inductance M is the result of the interaction of ribbons 16, 18 and 19 between them.

The response curve of this modeled antenna, depending on the frequency, real part R (f) and imaginary part X (f), is illustrated on the figure 3.

Reference is made to this FIG. 3, on the one hand the evolution of the response on the fundamental mode and secondly the evolution of the answer at the level of parallel resonance related to the original operating principle of such antennas. The latter results in a peak of resonance for the real part R (f) and by an oscillation for the imaginary part X (f).

This resonance peak of the input impedance of the antenna is the consequence of the capacitive effect of the two plates 12 and 14 and the effects of inductive and mutual induction of the ribbons 16, 18 and 19. Those skilled in the art will evaluate these elements by approximating the quasi-static state.

The operating band of the antenna is around cancellation frequencies of the imaginary part X (f) of the input impedance and corresponds to a real part R (f) around that of the generator 20.

Most of the radiation emitted by the antenna comes from the ribbon (s) 18, 19 and corresponds to quasi dipole type radiation omnidirectional in the plane perpendicular to the ribbons and whose polarization in this plane is parallel to the ribbons. It's the radiation classical electric dipole in a plane perpendicular to it. This dipole would be parallel to wires 16 and 18.

As previously suggested a dielectric substrate can be added on and / or under the metal plane defined by elements 12 to 19, to solidify the structure, to reduce the dimensions of the antenna by compared to the operating wavelength, to generate a radiation in the dielectric, etc.

In addition, a proximity reflector may be associated with the antenna to conform the radiation, for example to focus the radiation in a desired direction.

We will now describe the particular embodiment illustrated on Figure 4.

The antenna 10 illustrated in this FIG. 4 is formed by cutting into a metal sheet with a thickness of 0.4 mm.

It comprises a roof 12 with a square geometry of 25 mm × 25 mm, be of the order of λ / 12 × λ / 12.

The ground plane 14 is formed of a ribbon with a width of 6 mm, is of the order of λ / 50, and square geometry that surrounds almost totally the roof 12.

Thus the ground plane 14 is formed of four straight sections of ribbon, perpendicular and parallel to each other in pairs, possessing typically each an outer length of 65 mm, being of the order of λ / 5, and a width of 6 mm, ie of the order of λ / 50.

The roof 12 is preferably centered on the ground plane 14 and has its sides parallel to the sections of the ribbon forming this ground plane 14. Thus the distance separating the inner edge of the ground plane 14 and the outer edge roof 12, is of the order of 14 mm.

One of the aforementioned sections forming the ground plane 14 has a transverse cut 15 with a width of the order of 5 to 8 mm.

This cutout 15 is preferably formed at about 37 mm from a end of this stretch and about 23 mm from the other end of the same stretch of ground plane.

A rectilinear mass tape 18 with a width of 8mm and a length of the order of 14 mm connects the inner edge of the section 14 having the cutout 15 and the roof 12. This mass tape 18 thus extends perpendicular to section 14 and at the edge of roof 12. This ribbon mass 18 is preferably connected to the longest element of the ribbon 14 having the cutout 15 and is preferably connected to the roof at a distance of about 4 mm from one of the angles thereof.

The supply ribbon 16 is formed of a rectilinear ribbon, centered on the cutout 15, of a width of the order 3 mm and which is connected perpendicularly to one side of the roof 12, preferably at a distance an angle thereof of the order of 4 mm.

It can be seen in FIG. 4 that the section of the ribbon 14 having the cutout 15 is provided with a connector 30 whose shielding external connection is electrically connected to the grounding strip 14 and whose strand is central conductor is connected by any suitable means to the end outer ribbon 16.

FIG. 5 represents the real part R (f) of the input impedance of the antenna 10 illustrated in FIG. 4, in Ω, as a function of the frequency.

Figure 6 shows the imaginary part X (f) of the impedance of the same antenna 10 illustrated in FIG. 4, in Ω, in function of the frequency.

And FIG. 7 shows the reflection coefficient | S ₁₁ | resulting from it.

More precisely in FIGS. 5 to 7, there is illustrated in solid lines the theoretical curves and in broken lines the actual curves measured on an antenna according to Figure 4.

The reflection coefficient | S ₁₁ | theoretical is minimal (- 28 dB) at 1.057 GHz and the reflection coefficient | S ₁₁ | actual measured is minimal (- 21.3 dB) at 1.07 GHz.

The overall dimensions of the device 10: antenna plus plane of mass, illustrated in Figure 4, are of the order of λ / 6 to λ / 5 where λ is the working wavelength.

The intrinsic gain at the frequency of 1.06 GHz shown in the figures 8 to 10 reflects an almost omnidirectional radiation in the plane orthogonal to ribbons 18, 19, in accordance with the radiation principle of the dipole.

FIG. 8 represents the gain as a function of the angle  between direction of observation and a perpendicular to the metal plane, in the ribbon plane 16 (ie φ = 0 °).

FIG. 9 represents the gain as a function of the angle  between the direction of observation and a perpendicular to the metal plane, in a plane perpendicular to the ribbon 16 (ie φ = 90 °).

Figure 10 shows the gain in the plane of the antenna ( = 90 °) in function of the azimuth φ of observation in this plane.

There are a large number of known antennas, including antennas planar.

1) les structures résonantes planaires type « microrubans » composées d'éléments empilés avec au moins deux niveaux de métallisation par exemple un plan de masse, un substrat diélectrique qui peut être de l'air et un élément rayonnant métallique; appartiennent à cette famille par exemple

• les antennes « patch » rayonnantes basées sur le principe des cavités résonantes à fuites générant des bandes de fonctionnement étroites (dont la dimension est au moins de l'ordre de λg/2, λg représentant la longueur d'onde dans le diélectrique) et
• les antennes « fil-plaque » microruban, telles que décrites dans le document EP-A-667 984 de même structure que les antennes patch précédentes mais qui travaillent sur un principe différent et qui permettent une adaptation à des fréquences voisines de λ/8, et

2) les structures « planaires » qui ne comportent qu'un élément plan métallique qui constitue l'antenne, associé généralement à un substrat diélectrique pour rigidifier l'ensemble: ces antennes ne nécessitent à priori pas de plan de masse, mais sont la plupart du temps disposées parallèlement à un tel plan pour permettre une alimentation correcte.

Appartiennent à cette seconde famille par exemple :

• les dipôles électriques et magnétiques résonants dans leur version imprimée sur substrat , qui ne diffèrent des antennes « patch » que par le mode de résonance qui est celui d'une plaque métallique et non d'une cavité,
• les antennes à fentes résonantes, et
• les structures planaires à ondes progressives constituées de tronçons de lignes microruban ou coplanaires adaptées aux extrémités, la caractéristique principale de ces antennes est leur grande dimension par rapport à la longueur d'onde pour obtenir un bon rendement.

By way of non-limiting examples, mention may be made of:

1) planar resonant structures "microstrips" composed of elements stacked with at least two metallization levels, for example a ground plane, a dielectric substrate which may be air and a metallic radiating element; belong to this family for example

• radiant "patch" antennas based on the principle of resonant leak cavities generating narrow operating bands (whose dimension is at least of the order of λg / 2, λg representing the wavelength in the dielectric) and
• microstrip "wire-plate" antennas, as described in document EP-A-667 984 of the same structure as the previous patch antennas but which work on a different principle and which allow an adaptation to frequencies close to λ / 8, and

2) the "planar" structures which comprise only a metallic plane element which constitutes the antenna, generally associated with a dielectric substrate to stiffen the assembly: these antennas do not require a prior mass plane, but are most of time arranged parallel to such a plane to allow a correct power supply.

Belong to this second family for example:

• the resonant electrical and magnetic dipoles in their printed version on a substrate, which differ from the "patch" antennas only in the resonance mode which is that of a metal plate and not of a cavity,
• antennas with resonant slots, and
• the planar traveling wave structures consist of microstrip or coplanar line sections adapted to the ends, the main characteristic of these antennas is their large dimension relative to the wavelength to obtain a good performance.

• dimension d'antenne petite par rapport à la longueur d'onde, soit de l'ordre de λ/6 à λ/5, plan de masse compris,
• antenne planaire et ne possédant qu'une très faible épaisseur,
• large bande de fréquences par rapport aux antennes résonantes classiques,
• rayonnement dipolaire dans l'espace,
• association facile de plans de masse et de substrats.

Thus the inventors do not know any existing antenna corresponding to the structure according to the present invention previously defined and having in particular the following advantages:

• small antenna size with respect to the wavelength, ie of the order of λ / 6 to λ / 5, including ground plane,
• planar antenna and having only a very small thickness,
• wide band of frequencies compared to conventional resonant antennas,
• dipole radiation in space,
• easy association of mass planes and substrates.

It will also be noted that the present invention enables the realization antennas at very low cost, with great ease of realization.

The present invention can find application in a large number domains. As non-limiting examples, the antennas for automobiles, antennas for wireless links, millimeter antennas for sectorial distribution, sources of "lentils" antennas and "Dishes", antennas for wireless telephony, etc.

Of course, the present invention is not limited to the mode of particular embodiment which has just been described. Advantageously, for certain applications where the radiation is desired directional in the plane φ = 0 and no longer omnidirectional, we can add to the antenna a reflective plane which is parallel and located at a distance of the order of λ / 20.

According to the embodiment shown diagrammatically in FIG. strips 16, 17 connecting the generator / receiver 20 and respectively the first surface 12 and the second surface 14 are coplanaries of the latter. According to the schematic embodiment on FIG. 4, only the ribbon 16 connecting the generator / receiver 20 and the first surface 12 is coplanar with the surfaces 12 and 14, the connection between the generator / receiver 20 and the second surface 14 being ensured directly via the mass of a coaxial plug. In variant, however, it can be envisaged that neither the ribbon 16 nor the ribbon 17 coplanar surfaces 12 and 14. For this we can for example provide a supply of said surfaces 12, 14, from above.

According to yet another variant, the surface 12 forming a roof can be split into several coplanar elements, or even be perforated, as indicated in EP-A-667984.

Claims (15)

1. Antenna of the type comprising:

   a first electrically conductive surface (12),

   a second electrically conductive surface (14) forming a ground plane, parallel to the first surface,

   a first electrically conductive feed wire or strip (16) which links a first terminal of a generator/receiver (20) to the first surface (12) and a second feed wire or strip (17) which links a second terminal of the generator/receiver (20) to the second surface (14), and

   at least one electrically conductive wire or strip (18, 19) which links the two aforesaid surfaces (12, 14),

   characterized in that the two surfaces (12, 14) and the wire(s) or strip(s) (18, 19) for linking these surfaces are all coplanar.
2. Antenna according to Claim 1, characterized in that at least the wire or strip (16) ensuring the link between the generator/receiver (20) and the first surface (12) is also coplanar with the surfaces (12, 14).
3. Antenna according to one of Claims 1 or 2, characterized in that the wire or strip (17) ensuring the link between the generator/receiver (20) and the second surface (14) is also coplanar with the surfaces (12, 14).
4. Antenna according to one of Claims 1 or 3, characterized in that the second surface (14) forming a ground plane, at least partially surrounds the first surface (12).
5. Antenna according to one of Claims 1 to 4, characterized in that the second surface forming a ground plane (14) has the shape of an open ring which almost totally surrounds the first surface (12).
6. Antenna according to one of Claims 4 or 5, characterized in that the opening (15) made in the ground plane (14) serves for passing the wire or strip (16) ensuring the link between the generator/receiver (20) and the first surface (12).
7. Antenna according to one of Claims 1 to 6, characterized in that it comprises at least two wires or strips (18, 19) linking together the first and second surfaces (12, 14).
8. Antenna according to one of Claims 1 to 7, characterized in that it is made by cutting out from a conductive plane a preferably metal plate, for example by etching the metallization of a single-sided printed circuit, or else by screen-printing onto an electrically insulating support, deposition on such an electrically insulating support, or production from a metal foil of suitable geometry.
9. Antenna according to one of Claims 1 to 8, characterized in that its dimensions in the plane of the surfaces (12, 14) are of the order of λ/6 to λ/5 where λ represents the working wavelength.
10. Antenna according to one of Claims 1 to 9, characterized in that it comprises a dielectric substrate on and/or under the plane of the first and second surfaces (12, 14).
11. Antenna according to one of Claims 1 to 10, characterized in that it furthermore comprises an associated proximity reflector for shaping the radiation, for example for concentrating the radiation in a desired direction.
12. Antenna according to one of Claims 1 to 11, characterized in that it comprises a first surface (12) of square geometry and a ground plane (14) formed of four rectilinear segments of strip, perpendicular and parallel to one another pair-wise, which almost totally surrounds the first surface (12), one of the aforesaid segments forming the ground plane (14) possessing a transverse cutout (15) for the passage of a strip (16) ensuring the link between the generator/receiver (20) and the first surface (12).
13. Antenna according to Claim 12, characterized in that it furthermore comprises a rectilinear ground strip (18) which links the inner edge of the segment (14) possessing the cutout (15) and the first surface (12) and extends perpendicularly to their edges.
14. Antenna according to one of Claims 12 or 13, characterized in that it comprises a first surface (12) of square geometry whose sides have a length of the order of λ/12 and a ground plane (14) formed of four rectilinear segments of strip, perpendicular and parallel to one another pair-wise, of a length of the order of λ/5 and of a width of the order of λ/50, which almost totally surrounds the first surface (12).
15. Antenna according to one of Claims 1 to 14, characterized in that it comprises a connector (30) whose outer shielding is joined electrically to the ground plane (14) and whose central conductive rod is joined to the strip (16) ensuring the link between the generator/receiver (20) and the first surface (12).

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